There are previously known different embodiments of control systems for the control of heating cables or the like for snow and ice melting at roof downpipes, in gutters and the like. In principle, two control systems are on the market today. One of these measures the air temperature and connects heating cables in an adjustable temperature interval, e.g. between -5 and +5.degree. C. The other system measures an air temperature and combines this with a water sensor in a gutter, and a heating cable is kept connected as long as the temperature is below the melting point at the same time as the water sensor registers moisture in the gutter.
The weakness of the first system is that it uses much current. The second system will be connected as long as one has minus degrees and snow. However, much dirt always gathers in gutters, something which may rapidly cause errors in the water sensor registration.